In the broadcasting and communication fields, data is transmitted by a block having a given length such as frame. A receiving device detects an identifier, such as a frame synchronization signal, stored in the transmission data by a frame, establishes frame synchronization thereby and executes demodulation processing by the frame.
For example, in DTMB (Digital Terrestrial Multimedia Broadcast), which is a terrestrial digital broadcasting standard of China (People's Republic of China), a frame is composed of a frame body (hereinafter also referred to as an FB) and a frame header (hereinafter also referred to as an FH). The frame body stores 3780 symbols in which modulated source stream data and system information are combined. The frame header stores a known pseudo random noise sequence (hereinafter referred to as a PN sequence) which identifies a frame.
The PN sequence of the frame header is generated by an LFSR (linear feedback shift register). The LFSR can generate a known PN sequence having periodicity and in an FH mode 1, for example, a known frame header is obtained by circulating and expanding a generation sequence PN255 defined by a generating polynominal. Since the frame header is a known PN sequence, the frame header is used not only in detection of frame synchronization but also used as a pilot signal and can be used in demodulation processing such as channel response estimation or the like.
As a method of detecting the clock frequency error in reception of a signal of the DTMB broadcasting standard and of performing clock regeneration, a pattern matching method can be considered. If there is a clock frequency error, detection timing of a correlation peak obtained by the pattern matching is shifted. Clock regeneration is realized by detecting the shift in detection timing of the correlation peak so as to estimate a clock frequency error.
However, since the position of the PN sequence is changed for each initial value (frame number) of the LFSR, it cannot be discriminated whether a cause of the shift in detection timing of the correlation peak comes from a difference of a frame number or a clock frequency error, until super frame synchronization is established. Thus, the super frame synchronization should be established first in order to perform clock regeneration. Alternatively, a method of averaging the correlation peak detection timing by a super frame in order to detect the clock frequency error. In any case, the detection of the clock frequency error takes time, and there is a problem that clock regeneration takes a long time.
Moreover, if there is multipath interference, the correlation peak caused by the multipath interference might be used for detection of the clock frequency error, and there is a problem that the clock frequency error might be erroneously detected.